Project Summary/Abstract ? Project 2 Pelvic organ prolapse (POP), descent of the pelvic organs (bowel, bladder, uterus) into the vagina, and pelvic floor symptoms such as urinary incontinence, are common and costly conditions that impact the health and well being of millions of women world-wide. For many women, the stage for future pelvic floor disorders is set with the first vaginal delivery, yet we know little about how to maximize recovery following this seminal event. The long-term goal of this research is to develop evidence-based interventions that mitigate the impact of vaginal delivery on key indices of pelvic floor health. In this project, we plan to study how physical activity, sedentary time, measures of muscular strength and body habitus impact two primary outcomes: pelvic floor support and pelvic floor symptoms. Young women demonstrate a range of vaginal support and pelvic symptomatology during the first postpartum year, but little is known about why they differ from each other. By drawing parallels between vaginal delivery and other acute soft tissue injuries, this project will explore biologically plausible factors known about muscle and connective tissue healing that may be related to postpartum recovery and thereby pelvic floor health: timing, dose and type of physical activities, muscular strength and body habitus. We hypothesize that the early postpartum period (first 8 weeks) reflects acute healing and early recovery when moderate to vigorous physical activity (MVPA, measured using accelerometry) may impair healing and result in worse pelvic floor support and greater symptoms one year postpartum. Conversely, the remaining first postpartum year reflects a period to strengthen and improve supporting structures; we hypothesize that greater MVPA and less sedentary time will improve pelvic floor support and reduce symptoms. The scope of this project is relevant to NICHD's described mission, to ensure that ?women suffer no harmful effects from reproductive processes, and?to ensure the health, productivity, independence, and well-being of all people through optimal rehabilitation?, and specifically addresses pelvic floor disorders, as emphasized in the portfolio of the Gynecologic Health and Disease Branch. This prospective cohort study will recruit 1530 nulliparous women in the third trimester of pregnancy and follow those that deliver vaginally for 1 year postpartum. The aims of this project are to study the effect of 1) physical activity and inactivity, 2) muscular strength, and 3) body habitus, all measured in the early and later postpartum periods, on pelvic floor support and symptoms one year postpartum. We will also explore whether the presence of a high-risk delivery variable (forceps, prolonged 2nd stage of labor, shoulder dystocia, anal sphincter laceration) modifies the association between MVPA in the early postpartum period on pelvic floor support and symptoms at 1 year.